(a) Field of the Invention
The present invention relates to a manufacturing method of a printed circuit board using a dry film resist and, more particularly, to a manufacturing method of a printed circuit board using a dry film resist in forming a circuit pattern on a copper overlaid laminate as a normal printed circuit board, in which a modification of the manufacturing process can enhance the resolution and fine weldability of the resist to realize a minimization of the circuit pattern.
(b) Description of the Related Art
In general, a dry film resist (hereinafter, referred to as xe2x80x9cDFRxe2x80x9d) is used in forming a circuit pattern on a printed circuit board (hereinafter, referred to as xe2x80x9cPCBxe2x80x9d). The manufacturing method of a PCB using a DFR is schematically shown in FIG. 1.
To form a copper overlaid laminate as a substrate of the, PCB, a pretreatment is performed, in step 10. The pretreatment comprises an outer layer processing step that sequentially includes drilling, deburing and facade, and an inner layer processing step including counter etching or acid rinsing.
Following, the pretreatment, a DFR is laminated on a copper layer of the copper overlaid laminate to form a circuit pattern on the copper overlaid laminate, in step 20. In this lamination step, use is made of a laminator to peel a protective film of the DFR and laminate a resist layer of the DFR on the surface of the copper layer. Typically, lamination is performed under conditions: the lamination rate 0.5 to 3.5 m/min, the temperature 100 to 130xc2x0 C., the pressure of a heating roller 10 to 90 psi.
Subsequent to the lamination, the PCB is kept for over 15 minutes to stabilize the substrate, in step 30, and the resist layer of the DFR is subjected to exposure using a photomask in which a desired circuit pattern is formed, in step 40. During the exposure, the UV ray irradiated on the photomask causes a photoinitiator contained in the exposed area of the resist to activate polymerization in the resist. The oxygen in the resist is consumed to polymerize active monomers and cause crosslinking and then polymerization with a large amount of monomers. Contrarily, the crosslinking hardly occurs in the unexposed area of the resist.
Subsequently, development is performed to eliminate the unexposed areas of the resist, in step 50. In the development step, an aqueous solution containing 0.8 to 1.2 wt. % of potassium carbonate or sodium carbonate is used as a developing agent for an alkaline-developed DFR. Meanwhile, the unexposed areas of the resist are washed away due to saponification of the carboxylic acids of the binder contained in the developing agent, remaining the cured resist on the surface of the copper layer.
Inner and outer layer processing steps are performed to form a circuit pattern, in step 60. The inner layer processing step includes corrosion and stripping to form a circuit pattern on the substrate, and the outer layer processing step includes etching and solder stripping after plating and tending to form a defined circuit pattern.
When patterning a circuit on the PCB using a DFR, the circuit pattern thus formed may have a line width of 0.1 mm as possible. With the recent tendency of electronic equipment, including miniaturization, light-weight, high performance and high reliability, there is a keen need for densification, high performance and high precision of the PCB used in the electronic equipment as well as a method for reducing the line width of the circuit pattern. Hence, the resolution and fine weldability of the DFR are also required.
To improve the resolution and fine weldability of the DFR, the inventors of this patent have contrived a so-called post-exposure heating process that includes an annealing step between exposure of the resist and elimination of the unexposed areas of the resist, which process has been applied (Korean Patent Application No. 98-14380) and granted (Korean Patent No. 271216).
Now, the post-exposure heating process will be described in detail with reference to FIG. 2.
First, a substrate is subjected to a pretreatment in the same manner as described above with reference to FIG. 1, in step 10. Following the pretreatment, a DFR is laminated on the top surface of the substrate, in step 20, and kept for a while, in step 30. The DFR is then exposed to the UV radiation with a photomask to form a desired circuit pattern, in step 40.
Subsequently, the resulting material is annealed, in step 45. The annealing is performed with a heating roller or a hot air oven, which is known to the skilled in the art. The annealing with a heating roller is performed under conditions that satisfy at least one of the following requirements: using 1 to 3 heating rollers, the temperature of the heating roller 80 to 160xc2x0 C., the driving rate of the heating roller 0.2 to 5.0 m/min, and the pressure of the heating roller 10 to 90 psi. The annealing with a hot air oven is performed at the oven temperature 80 to 200xc2x0 C. for 5 to 600 seconds.
Although the post-exposure heating process for improving resolution and fine weldability of the resist may enhance the fundamental properties of the dry film, the use of a hot air oven deteriorates workability and productivity and that of a heating roller requires a strict control of the process because the contamination of the heating roller with foreign materials may increase fixing-related defectives.
In an attempt to solve the problems with the post-exposure heating process, the inventors of this invention found out that the use of an infrared (IR) drying zone instead of a heating roller or a hot air oven can reduce fixing-related defectives caused by foreign materials during the process and improve the efficiency of production as well as achieve defined objects of the annealing.
It is an object of the present invention to provide a method for reducing fixing-related defectives caused by foreign materials and improving the efficiency of production in performing an annealing step subsequent to exposure in the manufacture of a printed circuit board (PCB) or lead frames using a dry film resist (DFR).
It is another object of the present invention to demonstrate the effect of using a DFR having a predetermined thickness in performing an annealing step subsequent to a so-called post-exposure heating process using a rolling roll, a hot air oven or an IR drying zone.
To achieve the objects of the present invention, there is provided a manufacturing method of a PCB and a lead frame using a DFR that includes pretreatment, lamination, keeping, exposure and development, wherein the manufacturing method further includes a heat drying step performed with an IR drying zone for 5 to 600 seconds between the exposure of the resist and the removal of unexposed areas of the resist.
In another aspect of the present invention, there is provided a manufacturing method of a PCB that includes an annealing step between a step of exposing the resist having a thickness in the following range and a step of moving unexposed areas of the resist:
5xcexcmxe2x89xa6txe2x89xa6100xcexcm
where t represents the thickness of a resist layer between base and cover films of the DFR, provided that 20 xcexcmxe2x89xa6txe2x89xa630 xcexcm is excluded.
Hereinafter, the manufacturing method of the present invention will be described in detail with reference to FIG. 3.
The procedures are performed in the same manner as the conventional manufacturing method that includes pretreatment (step 10), lamination (step 20), keeping (step 30) and exposure (step 40). Subsequently, heat drying is performed with an IR drying zone (step 45xe2x80x2).
The heat drying is performed with the IR drying zone 30 to 300 cm long at a temperature of 30 to 150xc2x0 C. for 5 to 600 seconds, under which conditions heat curing of the resist hardly occurs.
The heat drying conditions may be summarized as follows:
30 cmxe2x89xa6Lxe2x89xa6300 cm, 30xc2x0 C.xe2x89xa6Txe2x89xa6150xc2x0 C., and 5 sec.xe2x89xa6txe2x89xa6600 sec.
where L is the length of the IR drying zone, T the temperature of the drying zone, t the detention time of the IR drying zone.
Under conditions beyond the above range, the resist is not sufficiently annealed as to have enhanced fine weldability and resolution. Also, excessive annealing may lea cause heat curing of the unexposed areas of the resist and hence insufficient development and stripping on the resist during the subsequent development and stripping steps.
The subsequent steps are development (step 50) and inner/outer layer processing (step 60).
The annealing with an IR drying zone in the continuous manufacturing process of a PCB solves the problem of fixing-related defectives that may increase in the annealing step using a heating roller due to contamination of the heating roller as shown in FIG. 2. Such an annealing step with an IR drying zone also increases the drying efficiency than the annealing with a hot air oven, thus reducing the annealing time with a high efficiency and enhancing the properties of the circuit pattern, such as sensitivity, resolution and fine weldability.
On the other hand, the present invention further includes annealing using a heating roller or a hot air oven in a defined thickness range of the resist as well as the above-mentioned annealing using an IR drying zone.
The annealing using a heating roller is performed under conditions that satisfy at least one of the following requirements: using 1 to 3 heating rolls, the temperature of the heating roller 80 to 160xc2x0 C., the driving rate of the heating roller 0.2 to 5.0 m/min, and the pressure of the heating roller 10 to 90 psi. The annealing with a hot air oven is performed at an oven temperature of 80 to 200xc2x0 C. for 5 to 600 seconds.
The effect of annealing on the DFR is dependent on the thickness of the resist layer of the DFR. That is, the annealing on a thin film or a thick film remarkably enhances the fundamental properties of the DFR, such as independent thinning, resolution and follow-up ability.
Preferably, the resist layer of the DFR has a thickness of about 5 to 100 xcexcm, excluding the thickness range of 20 to 30 xcexcm.
The so-called xe2x80x9cthin DFR (Dry Film Resist)xe2x80x9d has a resist layer of which the thickness is equal to or greater than 5 xcexcm and less than 20 xcexcm. The DFR having a resist layer that is greater than 30 xcexcm and less than or equal to 100 xcexcm in thickness is called xe2x80x9cthick DFRxe2x80x9d.
The annealing remarkably enhances the fundamental properties of a thin or thick DFR, such as resolution or fine weldability, and especially increases the follow-up ability of the DFR, which contributes to an increase in the production yield.
Following the annealing step, development and inner/outer layer processing are performed.